INDIANAPOLIS — Suspended driver AJ Allmendinger will enter NASCAR's Road to Recovery program, where he will be prescribed a path to reinstatement by a substance abuse professional after he tested positive for amphetamines, his business manager said.

Allmendinger, already under a temporary NASCAR suspension since July 7, was indefinitely suspended Tuesday night for a June 29 drug test that was a positive for a banned substance. The positive test was confirmed after Allmendinger's B sample was tested on Tuesday.

Allmendinger's business manager, Tara Ragan, said in an interview Wednesday night that Allmendinger tested positive for an amphetamine and that while it was not any sort of illegal drug such as methamphetamine or Ecstasy, they did not know the exact amphetamine compound for which he tested positive.

“Within amphetamines is a whole list of items,” Ragan said. “We’re trying to get to what it is. … We do know that it’s not cocaine, it’s not methamphetamine, it’s not Ecstasy, it’s not alcohol, it’s not marijuana.”

Ragan said that Allmendinger is working with an independent laboratory to figure out what caused the positive result.

"While we await further information from testing to determine the cause, we have notified NASCAR that AJ will participate in the Road to Recovery Program starting immediately," Ragan said in a statement Wednesday. "As we have stated earlier, we respect NASCAR's drug testing policies. They are first and foremost in place to protect drivers and AJ being among those. We fully support the program and as more details become available, we will share them."

"I just want to say, ‘Thank you' first and foremost for all of you sticking by me," he wrote in his tweet. "Please don't think me being (quiet) means I haven't been reading all (of) your support. And man, it means more than you will ever know.

"I'm sorry we even have to have this going on. But I promise I will do whatever it takes to get to the bottom of this and get back out there no matter what. Thanks guys."

The recovery program requires Allmendinger to meet with a substance abuse professional, who will create a plan for his return to the sport. The plan could include counseling or treatment at a rehabilitation facility. NASCAR would do additional drug testing before his return to competition.

The program could take anywhere from a few weeks to a few months or even longer, depending on the substance abuse professional's evaluation and the drug involved.

"We're very pleased that AJ Allmendinger has chosen to participate in the NASCAR Road to Recovery program," NASCAR spokesman David Higdon said in a statement Wednesday. "It's designed, as proven, to provide a roadmap leading to a return to competition, and we wish him the best of luck. As we have with other competitors, we look forward to the day when the Program Administrator recommends him for reinstatement."

NASCAR has not disclosed the drug Allmendinger tested positive for, and Higdon would not confirm Wednesday whether it was for amphetamines. He did say that while Ragan had said Allmendinger was only nanograms beyond the acceptable threshold that the test results showed that Allmendinger was much more than just slightly over the NASCAR threshold.

Higdon said Tuesday that the amount beyond the threshold does not matter when determining whether to suspend a competitor. He said that NASCAR did not obtain any new information from Allmendinger's B sample that would cause it to determine that it wasn't a positive test.

Ragan said Wednesday that Allmendinger will have his supplements and medications analyzed to determine if they could have resulted in the positive test. That process can’t start until Allmendinger gets the detailed test results, which a driver doesn’t receive until a day or two after the B sample is analyzed.

“We really don’t know what we’re looking for,” Ragan said. “We need to know what has happened or what he has been exposed to so it doesn’t happen again and we’re educated on it.

“We’re going to continue down that path because we want to know what happened. … We’re going to chase that down to the best of our ability so we can know what may have transpired, what it was and how to deal with it.”

Ragan said it was better for Allmendinger to start the recovery program while he tries to figure out what happened. She said he hopes to return to racing later this month but he has not heard from NASCAR about how long the recovery program will last.

“The No. 1 goal is to get AJ back in the 22 car,” she said. “Let’s exhaust every resource that is given to us and provided to us so we can do that as quickly as possible. … AJ is very committed to getting back in that car so why sit here and wait?”

Allmendinger had a toxicologist watch the testing of his B sample Tuesday and the toxicologist determined that everything done in the lab was OK, Ragan said. They will get the chain of custody documents this week to determine if there could have been any contamination before ruling out everything except for a false positive.

Drivers are instructed by NASCAR to notify it of any drugs or supplements they take, and they can also list potential supplements that could generate a false positive at the time they provide a urine sample.

NASCAR warns against dietary supplements in its rulebook.

"Dietary supplements may contain (either purposefully or through contamination) a prohibited substance under this Policy," NASCAR rule 19-4-D states. "Any product sold with a warning advising non-use if the purchaser is subject to a drug testing program should be avoided even though such product may be available without a prescription."

Once he completes the Road to Recovery program, Allmendinger still must find a team to drive for as there is no guarantee that Penske Racing will retain him. His contract with the team is up after this season.

In a statement Tuesday night, Penske officials said they would determine Allmendinger's status later this week and sponsor Shell/Pennzoil said it would work with Penske.

"We share Penske Racing's disappointment with the result of AJ's B sample test and will work closely with them to determine plans moving forward," Shell/Pennzoil said in a statement. "We hope for the best for AJ during this difficult time."

Allmendinger also could race in another series. A former open-wheel driver, he is a co-owner of an IndyCar Series team and also won the Rolex 24 At Daytona, the season-opening race of the Grand-Am Rolex Sports Car Series.

NASCAR owns Grand-Am but no decision has been made on whether Allmendinger could race in Grand-Am event because he has not been on an entry list to race, Higdon said.

By applying for the Road To Recovery, Allmendinger has waived his right to appeal the suspension to NASCAR's appeals board.

No one has appealed a suspension as a result of violating the substance-abuse policy since NASCAR began allowing such appeals in 2010.